Nonwoven covered elastic fabrics are used in various industrial and consumer products sectors. In particular, webs of nonwoven elastic fabric are used to produce disposable sheets, disposable garments and hygiene and sanitary products, such as sanitary napkins, incontinence pads and baby diapers. However such webs typically do not have sufficient tear resistant strength to make them suitable for use as diaper side panels.
Several prior art patents describe different elastic fabric material that can be used for diaper side panels. For example, U.S. Pat. No. 5,674,216 to Buell et al describes the use of a zero strain laminate created by incremental stretching of laminate that has been assembled in the relaxed state. However, such a laminate may not have sufficient tear resistance for use in high stretch side panel applications.
Nonwoven covered elastic fabrics can be manufactured using various techniques. One process entails bonding, using hot melt adhesives or ultrasonics, a pre-made nonwoven of continuous filaments such as spunbond or discontinuous fibers (staple fibers) such as a thermobonded carded nonwoven, to an elastic film. The resulting laminate may be treated according to various techniques to yield an elastic laminate fabric. WO-A-9855295 describes a procedure for producing a composite material composed of two or three textile layers, wherein the fibers forming the textile layers are bonded and the layers are bonded to one another by means of a calender comprising a pair of engraved rollers. The rollers are produced and controlled for tip-to-tip operation, i.e. with all the protuberances of one roller in phase with the protuberances of the other roller, and form a pattern of bonding spots with a density corresponding to the density of the protuberances on the two rollers.
WO-A-0004215 describes a method for producing a nonwoven fabric by means of thermal consolidation of a web of fibers or filaments, such as a web of textile fibers, made of a thermoplastic material such as polypropylene. Bonding or consolidation is obtained through calendering with a roller provided with protuberances, which cooperates with a smooth roller.
U.S. Pat. No. 5,422,172 describes an elastic laminated sheet of an incrementally stretched nonwoven fibrous web and elastomeric film and a method of making the sheet. The elastic laminates are said to be useful in diapers, surgical gowns, sheets, dressing, hygienic products and the like.
While the above patents and applications disclose various methods for forming elastic laminates, many fall short of teaching a method to make an elastic laminate for diaper side panels that is tear resistant when subjected to high strain or stress. U.S. Pat. No. 6,942,748 describes an elastomeric film bonded between two or more layers of nonwoven webs formed of nonelastomeric thermoplastic fibers. The laminate is said to have in a predefined transverse direction, an elastic elongation value greater than the predefined elastic elongation value of the nonwoven webs, and an ultimate force to break in the predefined transverse direction of at least 3000 g/in. This patent provides higher weight nonwovens having high resistant to tearing, but teaches away from creating high stretch products using relatively low basis weight nonwovens. Since tear resistance is achieved by using highly bulked nonwovens, this process is not suitable for diaper side panels since it will inhibit anchoring the closure tape to the elastic film and require the use of a deadened zone to act as a linkage between the elastic laminate and the closure tape. Thus, there is a continuing need for an improved method to produce a diaper side elastic laminate having improved softness, compatibility with a tape closure, and high resistance to tearing.